---
name: "nexttowardf"
section: "3"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/nextafter"
---

# nexttowardf(3)

floating-point number manipulation

Part of [nextafter(3)](/nextafter/3.md).

## NAME

nextafter, nextafterf, nextafterl, nexttoward, nexttowardf, nexttowardl - floating-point number manipulation

## LIBRARY

Math library (*libm*, *-lm*)

## SYNOPSIS

```
#include <math.h>
```

**double nextafter(double** *x***, double** *y***);** **float nextafterf(float** *x***, float** *y***);** **long double nextafterl(long double** *x***, long double** *y***);**

**double nexttoward(double** *x***, long double** *y***);** **float nexttowardf(float** *x***, long double** *y***);** **long double nexttowardl(long double** *x***, long double** *y***);**

Feature Test Macro Requirements for glibc (see [**feature\_test\_macros**(7)](/feature_test_macros/7.md)):

**nextafter**():

```
    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
        || _XOPEN_SOURCE >= 500
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
```

**nextafterf**(), **nextafterl**():

```
    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
```

**nexttoward**(), **nexttowardf**(), **nexttowardl**():

```
    _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE
        || _POSIX_C_SOURCE >= 200112L
```

## DESCRIPTION

The **nextafter**(), **nextafterf**(), and **nextafterl**() functions return the next representable floating-point value following *x* in the direction of *y*. If *y* is less than *x*, these functions will return the largest representable number less than *x*.

If *x* equals *y*, the functions return *y*.

The **nexttoward**(), **nexttowardf**(), and **nexttowardl**() functions do the same as the corresponding **nextafter**() functions, except that they have a *long double* second argument.

## RETURN VALUE

On success, these functions return the next representable floating-point value after *x* in the direction of *y*.

If *x* equals *y*, then *y* (cast to the same type as *x*) is returned.

If *x* or *y* is a NaN, a NaN is returned.

If *x* is finite, and the result would overflow, a range error occurs, and the functions return **HUGE\_VAL**, **HUGE\_VALF**, or **HUGE\_VALL**, respectively, with the correct mathematical sign.

If *x* is not equal to *y*, and the correct function result would be subnormal, zero, or underflow, a range error occurs, and either the correct value (if it can be represented), or 0.0, is returned.

## ERRORS

See [**math\_error**(7)](/math_error/7.md) for information on how to determine whether an error has occurred when calling these functions.

The following errors can occur:

- Range error: result overflow

  *errno* is set to **ERANGE**. An overflow floating-point exception (**FE\_OVERFLOW**) is raised.

- Range error: result is subnormal or underflows

  *errno* is set to **ERANGE**. An underflow floating-point exception (**FE\_UNDERFLOW**) is raised.

## ATTRIBUTES

For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md).

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **nextafter**(), **nextafterf**(), **nextafterl**(), **nexttoward**(), **nexttowardf**(), **nexttowardl**() | Thread safety | MT-Safe |

## STANDARDS

C11, POSIX.1-2008.

This function is defined in IEC 559 (and the appendix with recommended functions in IEEE 754/IEEE 854).

## HISTORY

C99, POSIX.1-2001.

## BUGS

In glibc 2.5 and earlier, these functions do not raise an underflow floating-point (**FE\_UNDERFLOW**) exception when an underflow occurs.

Before glibc 2.23 these functions did not set *errno*.

## SEE ALSO

[**nearbyint**(3)](/nearbyint/3.md)